Most people have experienced that prickly, stinging sensation known as pins and needles – or paraesthesia, to be medically accurate. It usually occurs when pressure is applied to the affected area, which restricts the blood supply to the nerves in that area. The limb may feel numb while the pressure is still applied, but the tingling generally starts when the blood flow resumes and the nerves start to send signals back to the brain again. In time they should disappear once the blood flow returns to normal.
If pins and needles are a recurring problem over a long period of time, they are referred to as chronic pins and needles. In these circumstances advice should be sought from a medical professional, as this could mean there is an underlying serious condition such as multiple sclerosis or diabetes.
Rik Sargent, Science Museum